How much of the trigger did you take apart? Just that one pin that holds the trigger, or the whole thing?Also, I'm trying to remember if there was something tricky about that anti-beartrap lever and its spring. Does that look okay?
You can't let this beat you. Walk away and try again tomorrow. Make a shim from a soda bottle to keep the sear from popping inside the tube. And the spring does go outside the trigger pack. You have to push the trigger up and forward as you install it. This puts tension on the spring. Here's a pic of mine.
I checked "another air gun blog" as well, nothing on this Chinese model. They must have an assembly fixture at the factory, the trigger group has to be assembled in a few seconds to make these as cheap as they do. As many of them that are out there you would think there would be more info, but people probably just trash them.
On TV I saw a Chinese woman say, when asked, say yes, she thought China would put a man on the moon. Then when asked why she thought this, she said, "Because we have many, many hands." That's how they put these triggers together.